1. Field of the Invention
The present invention relates to a fluorescent substance and a method of manufacturing the fluorescent substance and a light emitting device using the fluorescent substance, and particularly to a fluorescent substance which contains oxygen and nitrogen and which is chemically stable, and to a method of manufacturing the fluorescent substance and to a light emitting device using the fluorescent substance.
2. Description of Related Art
A light emitting device capable of emitting light of various wavelengths by combining the light emitted from a light source and a fluorescent substance which is excited by the light from the light source and is capable of emitting light of different hue than the light from the light source, according to principle of mixing light has been developed. Examples of such a light emitting device include a white LED device which uses a blue semiconductor light emitting element and green to yellow light emitting yttrium-aluminum-garnet based fluorescent substance (Y3Al5O12:Ce). The white LED provides white light by color mixing of green to yellow light obtained by wavelength converting a part of blue light emitted from the light emitting element and blue light whose wavelength has not been converted. However, this system is unable to provide a sufficient amount of emission of visible light in long wavelength region, so that a white light of reddish hue such as an incandescent color cannot be obtained and it has low color rendering properties.
In contrast, a light emitting device employing a blue light emitting element and fluorescent substances which are excited by the blue light of the light emitting element and respectively emit light of green and red is capable of producing white light with good color rendering properties by additive color mixing of the three primary colors of light: blue, green, and red. Examples of the methods using additive color mixing of the three primary colors of light include a method in which a light emitting element capable of emitting near ultraviolet light is used to excite fluorescent substances of blue, green, and red colors by the near ultraviolet light emitted from the light emitting element and obtain a white light by the emissions from the respective fluorescent substances. As for a fluorescent substance applicable for such a light emitting device, a fluorescent substance capable of converting wavelength of light in the near ultraviolet region to a shorter wavelength range in the visible light region and emitting light of a longer wavelength range in visible light such as red light has been extensively developed.
For example, an oxynitride activated with a rare-earth element with which a higher brightness can be obtained in white LED having a blue LED light source is provided (for example, see JP 2002-363554A (Patent Reference 1)). The oxynitride fluorescent substance is represented by the formula MexSi12−(m+n)Al(m+n)OnN16−n:Re1yRe2z, in which a part or all of metal Me (where Me is at least one selected from Ca, Mg, Y, and lanthanide metals excluding La and Ce) in alpha-sialon solid solution is substituted by lanthanide metal Re1 (where Re1 is at least one selected from Ce, Pr, Eu, Tb, Yb and Er), or two lanthanide metals Re1 and a co-activator Re2 (where Re2 is Dy), to be an emission center. When the metal Me is bivalent, 0.6<m<3.0 and 0≦n<1.5. When the metal Me is trivalent, 0.9<m<4.5 and 0≦n<1.5. A fluorescent substance according to the present invention has different ratios of Al, Si, and N with respect to Me, so that it has a different composition than that of the oxynitride fluorescent substances described above.
Also, a fluorescent substance composition which is excitable by a near ultraviolet to blue light and emits a warm color light, especially a red color light is provided (for example, see JP 2005-48105A (Patent Reference 2). The fluorescent substance composition contains as a main component a composition represented by the composition formula: a((1−x−y)MO.xEuO.yCe2O3.bSi3N4.cAlN, and is made of a crystalline material, where M in the composition formula is at least one alkaline earth metal element selected from Mg, Ca, Sr, and Ba, and a, b, c, x, and y in the composition formula respectively satisfies 0.3≦a/(a+b)≦0.9, 0.2≦a/(a+c)≦0.8, 0.3≦c/(b+c)≦0.9, 0.2≦x≦0.2, 0≦y≦0.2, and 0.002≦x+y≦0.2.
However, the composition ranges of a, b, and c in the composition formula of the above fluorescent substance are not specified, so that appropriate disclosure of the invention has not been provided and thus the invention has not been sufficiently identified. Meanwhile, according to the examples of this patent reference, the ratio of N to M in the fluorescent compositions in Examples 1 to 18 and Examples 20 to 25 are different than that of the present invention, thus indicating different compositions. The fluorescent substance composition in Example 19 has a different ratio of Al to M than that of the present invention, thus having a different composition.
A fluorescent substance having an emission property with an emission peak wavelength in a range of 580 to 680 nm and high emission intensity, and having an excitation band property of a flat excitation band with high efficiency for excitation light in a broad wavelength range from ultraviolet to visible light has been provided (wavelength range from 250 nm to 550 nm) (for example, see JP2006-63323A (Patent Reference 3)). The fluorescent substance includes a product phase whose main phase showing a diffraction peak with relative intensity of 10% or more in the Bragg angle (2θ) range of 36.5° to 37.5° and 41.9° to 42.9° in X-ray diffraction pattern, when the relative intensity of the diffraction peak having a highest intensity in the X-ray powder diffraction pattern obtained with CoKα ray is defined as 100%. The product phase of the fluorescent substance is represented by the composition formula MmAaBbOoNn:Z, where element M is an element such as Ca, Sr, and Mg, element A is an element such as Al, element B is an element such as Si, O is oxygen, N is nitrogen, and element Z is an element such as Eu, satisfying n=2/3m+a+4/3b−2/3b−2/3o, m/(a+b)≧1/2, (o+n)/(a+b)>4/3, o≧0, and m:a:b=1:1:1. The ratios of M to A, B, and N are different in the above-described fluorescent substance and a fluorescent substance according to the present invention, which indicates different compositions.
A fluorescent substance that has a broad peak of an emission spectrum in a green to yellow range, has such a wide and flat excitation band that can realize the use of a wide range of light from near ultraviolet/ultraviolet light to blue light as excitation light has been provided (see for example WO 2006/093298 A (Patent Reference 4)). The fluorescent substance is represented by general formula MmAaBbOoNn:Z in which M is an element such as Ca, Sr, and Mg, A is an element such as Al, B is an element such as Si, O is oxygen, N is nitrogen, and Z is an element such as Eu, and 4.0<(a+b)/m<7.0, a/m≧0.5, b/a>2.5, n>o, n=2/3m+a+4/3b−2/3o. Upon excitation with light in a wavelength range of 300 nm to 500 nm, the fluorescent substance exhibits an emission spectrum having a peak wavelength range of 500 nm to 650 nm. However, the composition ranges of a, b, m, o, and n in the composition formula of the above fluorescent substance are not specified, so that appropriate disclosure of the invention has not been provided and thus the invention has not been sufficiently identified. Meanwhile, according to the above example, this fluorescent substance has ratios of A to M, or B to M and N to M which are different than that of the fluorescent substance according to the present invention, thus having a different composition.
A fluorescent substance having a broad emission spectrum in the blue region (peak wavelength of 400 nm to 500 nm) and a broad flat excitation band in the near ultraviolet/ultraviolet region has been provided (see for example, WO 2006/106883A (Patent Reference 5)). The fluorescent substance is represented by general formula MmAaBbOoNn:Z in which M is an element such as Ca, Sr, and Mg, A is an element such as Al, B is an element such as Si, O is oxygen, N is nitrogen, and Z is an element such as Eu, satisfying 5.0<(a+b)/m<9.0, 0≦a/m≦2.0, 0≦o<n=2/3m+a+4/3b−2/3o, and has an emission spectrum with a peak in the wavelength range from 400 nm to 500 nm under an excitation of the light in a wavelength range from 250 nm to 430 nm. However, the composition range of N with respect to N in the composition formula of the above fluorescent substance is not specified, so that appropriate disclosure of the invention has not been provided. Meanwhile, according to the above example, this fluorescent substance has a different ratio of N to M than that of a fluorescent substance according to the present invention, thus has a different composition. Also, this fluorescent substance emits light of blue color which is different emission color than a fluorescent substances of the present invention.
A fluorescent substance having higher brightness, an orange or red emission characteristic has been provided (see for example JP 2006-89547A (Patent Reference 6)). The fluorescent substance includes, as an active substance, a crystal represented by A2Si5−xAlxOxN8−x (in which A is one selected from Mg, Ca, Sr, and Ba, and x has a value of 0.05 to 0.8) to which a metal element M (M is an element such as Eu) is incorporated to form a solid solution. This fluorescent substance has ratios of Si, Al, O, and N with respect to A which are different than that of a fluorescent substance according to the present invention, thus having a different composition.
A green fluorescent substance which has higher brightness in green color than that of a conventional sialon fluorescent substance activated with a rare earth element and has superior durability than that of a conventional oxide fluorescent substance is provided (see for example JP 2005-255895A (Patent Reference 7)). The fluorescent substance is represented by Si6−zAlzOzN8−z (0<z<4.2) which includes a crystal of nitride or oxynitride having a β-type Si3N4 crystal structure having a metal element M (M is an element selected from Mn, Ce, and Eu) solid-dissolved into it, and emits a fluorescent light having a peak in a range of 500 nm to 600 nm in wavelength upon being irradiated with an excitation source. However, this fluorescent substance does not include elements such as Ca and Sr. Also, the above fluorescent substance and a fluorescent substance according to the present invention have different compositions. Also, this fluorescent substance emits light of green color which is a different emission color than that of a fluorescent substance according to the present invention.
A β-type sialon fluorescent substance which uses a light source of blue to ultraviolet light and is capable of realizing a white light emitting diode has been provided (see for example WO 2006/121083A (Patent Reference 8)). The above fluorescent substance is a β-type sialon fluorescent substance which includes a β-type sialon represented by general formula Si6−zAlzOzN8−z (0.24≦z≦4.2) as a matrix material and Eu in a solid solution form as a luminescent center. However, this fluorescent substance does not include elements such as Ca and Sr. Also, the above fluorescent substance and the fluorescent substances according to the present invention have different compositions. Further, this fluorescent substance emits light of green color which is a different emission color than that of the fluorescent substances according to the present invention.
A light source using a fluorescent substance capable of converting at least a part of the radiation of a primary light source to emit light of yellow to red color, in which the fluorescent substance has a host lattice of a nitridosilicate type MxSiyNz:Eu (in which M is at least one alkaline earth metal selected from the group consisting of Ca, Sr, Ba and Zn, and z=2/3x+4/3y, x=2 and y=5, or x=1 and y=7), has been disclosed (see for example WO 2001/40403A (Patent Reference 9)). However, this fluorescent substance does not include Al. Also, this fluorescent substance and a fluorescent substance according to the present invention have different compositions.
Further, CaS:Eu and Ln2O2S:Eu, for example, are known as a fluorescent substance capable of emitting long-wavelength visible light such as red light; however, they have poor chemical stability and show significant decline in brightness under a condition of high temperature. Such a fluorescent substance does not exhibit sufficient brightness as well. In recent years, a fluorescent substance, which has a favorable excitation band in a region of near ultraviolet to short wavelength visible light and is capable of converting a wavelength to obtain light of yellow to red color, and contains nitrogen which is chemically stable, has been developed. Examples of such a fluorescent substance containing nitrogen include Ca2Si5N8:Eu, and a light emitting device employing such a fluorescent substance to improve color rendering properties has been described (see for example JA 2007-142389A (Patent Reference 10)).
However, the above-described fluorescent substance containing nitrogen has a problem of significant reduction in brightness under a condition of high temperature. Also a fluorescent substance having poor thermal properties may cause color unevenness when it is employed in a light emitting device, because under a high temperature, the ratio of the fluorescent substance and other emission of different colors may differ largely in the mixed color of the emission.